/*
 * Copyright � 2002-2011 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

using System.Threading;

namespace Spring.Threading;

/// <summary> A latch is a boolean condition that is set at most once, ever.
/// Once a single release is issued, all acquires will pass.
/// <p>
/// <b>Sample usage.</b> Here are a set of classes that use
/// a latch as a start signal for a group of worker threads that
/// are created and started beforehand, and then later enabled.
/// </p>
/// <example>
/// class Worker implements IRunnable {
///   private readonly Latch startSignal;
///   Worker(Latch l)
///   {
///     startSignal = l;
///   }
///
///   public void Run() {
///     startSignal.acquire();
///     DoWork();
///   }
///
///   void DoWork() { ... }
///   }
///
///   class Driver { // ...
///     void Main() {
///       Latch go = new Latch();
///       for (int i = 0; i &lt; N; ++i) // make threads
///       new Thread(new ThreadStart(new Worker(go)).Start();
///       DoSomethingElse();         // don't let run yet
///       go.Release();              // let all threads proceed
/// }
/// }
/// </example>
/// </summary>
/// <author>Doug Lea</author>
/// <author>Federico Spinazzi (.Net)</author>
public class Latch : ISync
{
    /// <summary>
    /// can acquire ?
    /// </summary>
    protected bool latched_ = false;

    /// <summary>
    /// Method mainly used by clients who are trying to get the latch
    /// </summary>
    public void Acquire()
    {
        lock (this)
        {
            while (!latched_)
            {
                Monitor.Wait(this);
            }
        }
    }

    /// <summary>Wait at most msecs millisconds for a permit</summary>
    public bool Attempt(long msecs)
    {
        lock (this)
        {
            if (latched_)
            {
                return true;
            }
            else if (msecs <= 0)
            {
                return false;
            }
            else
            {
                long waitTime = msecs;
                //double start = new TimeSpan(DateTime.UtcNow.Ticks).TotalMilliseconds;
                double start = Utils.CurrentTimeMillis;
                for (;;)
                {
                    Monitor.Wait(this, TimeSpan.FromMilliseconds(waitTime));
                    if (latched_)
                    {
                        return true;
                    }
                    else
                    {
                        waitTime = (long) (msecs - (Utils.CurrentTimeMillis - start));
                        if (waitTime <= 0)
                        {
                            return false;
                        }
                    }
                }
            }
        }
    }

    /// <summary>
    /// Enable all current and future acquires to pass
    /// </summary>
    public void Release()
    {
        lock (this)
        {
            latched_ = true;
            Monitor.PulseAll(this);
        }
    }
}
